Sedimentation of particles in shear flows of fluids with fibers

The sedimentation of particles in a dense suspension supplemented by two additional factors is the subject of the current study. The addition of a small amount of thin flexible fibers into a base viscous suspending fluid is the first additional factor. The second additional factor is the subjection of the test fluid volume to shear flow in the plane perpendicular to the gravitational acceleration vector. Glycerol was used as the base Newtonian fluid. The mass fraction of monolithic synthetic fibers with length and diameter of 6 mm and 12 μm was varied from 0 to 0.4 %. Ceramic spheres with mean diameter of 0.66 mm were used to create suspensions with volume concentrations of 0–30 %. The sedimentation was observed in a transparent channel with a shear rate up to 108 s⁻¹. The sedimentation process was monitored by video recording and image processing techniques. It was found that fiber additives suppress the sedimentation significantly. The decrease in sedimentation velocity is more noticeable at low shear rates, whereas fibers do not markedly affect sedimentation at high shear rates of the order of 100 s⁻¹. The effect of the deceleration of the sedimentation increases as the fiber and particle concentrations increase. The linear relationship between the sedimentation velocity and viscosity of the suspension was demonstrated.